Arrayed optical fiber coupler and method of manufacturing the same

ABSTRACT

In a case where an arrayed optical fiber coupler obtained from a tape ribbon 1 is fixed to an reinforcement case 3, a glass portions 2b as a non-elongated portion outside of the elongated portions 2c of the coupler and a protection coating layers 2a at the back thereof are fixed to the reinforcement case 3 with an adhesive layer 4. A collectively coating resin layer 1a of the tape ribbon 1 is not fixed to the reinforcement case 3. The resin layer 1a is fixed to the reinforcement case 3 with a soft adhesive layer 5 different from the above adhesive layer 4, if necessary. As the resin of the adhesive layer 4, there is preferable an adhesive having the viscosity of 50 to 200 P and thermosetting property in addition to ultraviolet cure property.

FIELD OF THE INVENTION

The present invention relates to an arrayed optical fiber coupler inwhich 2n optical core fibers are melted, coupled and elongated and amethod of manufacturing the same.

BACKGROUND OF THE INVENTION

Generally, a conventional optical fiber coupler has a drawback that iteasily changes in characteristics and is damaged due to external forceor temperature change, because it has a small outer diameter portion ofa few tens of μm. Therefore, the conventional optical fiber coupler isdesigned such that the coupler for the melted, coupled and elongatedoptical fibers is fixed to a reinforcement substrate having a linearexpansion coefficient as much as quartz, so that the characteristics arestable.

As the reinforcement substrate, a plate member is used as described inJapanese Utility Model Application Laying-open No. 23408/1989 and a pipemember is used as described in Japanese Patent Application Laying-openNo. 63907/1989, for example.

On the other hand, thermosetting adhesive or ultraviolet cure adhesiveof epoxy, urethane acrylate, and cyanoacrylate is used as the adhesivefor adhering the conventional coupler.

Recently, a high density optical communication line has developed sothat the number of optical couplers increases. Therefore, since theconventional optical fiber coupler is designed to couple a pair ofoptical fibers to each other, there are caused problems that an occupiedarea by the optical fiber coupler increases and accommodation of excessportions at the ends of the optical fibers is complex.

On the contrary, as disclosed in Japanese Patent Application Laying-openNo. 295211/1990, for instance, the reinforcing method of the opticalfiber coupler is proposed in which after an optical fiber coupler forcoupling two optical fibers is fixed to a reinforcement member so that aplurality of reinforcement members are accommodated in a package, theoptical fibers are coupled outside of the package by a tape to constructan arrayed optical fiber coupler. Another method of reinforcing anoptical fiber coupler is proposed in which optical fiber couplers foreach coupling two optical fibers to each other are arranged on a fixingmember having a plurality of grooves in a comb manner, as disclosed inJapanese Patent Application Laying-open No. 254406/1988.

The methods disclosed in the above Japanese Patent ApplicationLaying-open No. 295211/1990 and Japanese Patent Application Laying-openNo. 254406/1988 are complicated and have a problem that it takes a longtime to form an arrayed optical fiber coupler because the optical fibercouplers for each coupling two optical fibers are mounted in a highdensity manner.

For this reason, as disclosed in Japanese Patent Application Laying-openNo. 120510/1990, the method is tried in which an arrayed optical fibercoupler is directly constituted from arrayed optical fiber ribbons. In acase that the arrayed optical fiber coupler is fixed to a reinforcementsubstrate, however, there is a problem that the transmissioncharacteristics are remarkably degraded due to temperature change orhumidity change.

FIGS. 10A, 10B and 10C show a reinforcement structure in a conventionalarrayed optical fiber coupler. FIG. 10A is a plan view of thereinforcement structure, FIG. 10B is a perspective view of areinforcement case used in the reinforcement structure shown in FIG.10A, and FIG. 10C is a cross sectional view of an arrayed optical fiberribbon used in the reinforcement structure shown in FIG. 10A. Areference numeral 1 denotes an arrayed optical fiber ribbon in FIG. 10C.This arrayed optical fiber ribbon 1 is constituted by collectivelycoating four optical fibers 2 each having a protection coating layer 2awith a coating layer 1a. A reference numeral 3 denotes a reinforcementcase in FIGS. 10A and 10B. 0n the upper surface 3a of the reinforcementcase 3, a pair of fixed walls 3b extending along a longitudinaldirection of the case in parallel to each other at both side edges areprovided to prevent the displacement of the optical fiber ribbon 1 bythe reinforcement structure.

In this arrayed optical fiber ribbon 1, after part of the coating layer1a and protection coating layer 2a of each optical fiber is removed toexpose a glass portion of the optical fiber 2, the ribbons 1 areoverlain in a vertical direction and corresponding glass portions 2b areheated and elongated to be melted and coupled. The glass portion 2b isfixed to the upper surface 3a and the fixed wall 3b of the reinforcementcase 3 by an adhesive layer 4, as well as the coating resin layer 1a ofthe optical fiber ribbon 1.

However, because distortion remained in the collectively coating resinlayer 1a from when the arrayed optical fiber ribbon 1 has beenmanufactured is released in a form of contraction of the collectivelycoating resin layer 1a due to temperature change or humidity change, arelative shift is caused between the collectively coating resin layer 1aand the glass portion 2b including a melted, bonded and elongatedportion. Thus, in the conventional arrayed optical fiber coupler,because the collectively coating resin layer 1a is strongly fixed to thereinforcement case 3, a stress is generated at a melted, bonded andelongated portion having a small diameter so that the transmissioncharacteristics of the optical fiber coupler is changed.

In a case where four or more optical fibers are collectively adhered andfixed to the reinforcement member, the optical fiber coupler does oftennot have sufficient circumstance resistance characteristics. Forinstance, an allowable change value is generally 0.2 dB or less in aheat cycle test in which temperature load of -20° to +60° C. is appliedto the optical fiber coupler to examine characteristics change. However,in the above structure, the change value of about 0.5 dB is oftenobserved, as shown in FIG. 11. The change value needs to be 0.2 dB orless after 100 hours in a characteristics change test under 60° C. and95%. In the above structure, the more than 0.3 dB change values arefrequently observed, as shown in FIG. 12. It should be noted that inFIG. 11 the abscissa represents time length of the heat cycle test, theordinate represents temperature in the heat cycle test and change valueof coupling loss due to the heat cycle test and that in FIG. 12 theabscissa represents time length during which a sample is exposed underhumidity and heat condition and the ordinate represents change value ofcoupling loss under the humidity and heat condition.

An object of the present invention is to provide an arrayed opticalfiber coupler and a method of manufacturing the same in which thearrayed optical fiber coupler has a reinforcement structure withsufficient circumstance resistance characteristics and, even if arelative shift is caused between a collectively coating resin layer anda glass portion of optical fiber ribbon because of distortion remainedin the collectively coating resin layer from when the optical fiberribbon is manufactured, a melted, coupled and elongated portion is notinfluenced due to the relative shift.

DISCLOSURE OF THE INVENTION

In order to achieve the object of the present invention, the inventiondefined in claim 1 is characterized by having a melted, bonded andelongated portion which is formed such that glass portions of an arrayedoptical fiber ribbon and another glass portions of another arrayedoptical fiber ribbon are melted, bonded and elongated in an opposingstate to each other, the arrayed optical fiber ribbon comprising aplurality of optical fibers being arranged in parallel to each other andbeing entirely coated with a collectively coating resin layer, each ofthe plurality of optical fibers including a glass portion and aprotection coating layer for protecting the glass portion, and by havinga reinforcement structure in which a peripheral glass portion and saidprotection coating layer are fixed to a reinforcement member.

The optical fiber includes one in which the protection coating layer isformed on a glass portion of the optical fiber which is composed ofquartz glass. As the protection coating layer, two layers coating istypically performed of a layer of soft material of a Young's modulus of1 Kg/mm² or less and a layer of hard material of a Young's modulus of 10Kg/mm². However, one layer coating or three layers coating may be used.In addition, a blue layer may be provided as the outermost layer of theprotection coating layer for identifying.

The arrayed optical fiber ribbon has the structure in which theplurality of optical fibers are arranged in parallel to each other andare coated with the collectively coating resin. The number of opticalfibers is 2, 4 or 8, for instance, but it is not limited.

Ultraviolet cure or thermosetting type resin is used for thecollectively coating resin layer but resin is not limited to them.

In the invention defined in claim 2, the reinforcement structure may befixed via the adhesive layer in the arrayed optical fiber couplerdefined in claim 1.

In the invention defined in claim 3, the coupler may have thereinforcement structure in which the collectively coating resin layer ofthe arrayed optical fiber ribbon is fixed to the reinforcement membervia an adhesive layer different from the adhesive layer via which thereinforcement structure is fixed in the arrayed optical fiber couplerdefined in claim 2.

In the invention defined in claim 4, the adhesive of the adhesive layervia which the collectively coating resin layer of the arrayed opticalfiber ribbon is fixed to the reinforcement member may have Young'smodulus of 1 Kg/mm² or less in the arrayed optical fiber coupler definedin claim 3.

In the invention defined in claim 5, the fixing of the arrayed opticalfiber ribbon to the reinforcement member includes only the fixing of theperipheral glass portions and the protection coating layers outside ofthe peripheral glass portions to the reinforcement member in the arrayedoptical fiber coupler defined claim 1 or 2.

In the invention defined in claim 6, the reinforcement member may havegrooves for each arranging the two optical fibers of the arrayed opticalfiber ribbon in parallel to each other in the arrayed optical fibercoupler defined in any one of claims 1 to 5.

In the invention defined in claim 7, the adhesive layer may be formed ofan adhesive having the viscosity of 50 to 200 P before cure in thearrayed optical fiber coupler defined in claim 2.

In the invention defined in claim 8, the adhesive layer may be formed ofan adhesive having the thermosetting property and the ultraviolet cureproperty in the arrayed optical fiber coupler defined in claim 2.

In the invention defined in claim 9, a method of manufacturing anarrayed optical fiber coupler characterized by comprising the steps ofremoving collectively coating resin layers and protection coating layersof middle portions of two arrayed optical fiber ribbons to expose glassportions, an optical fiber including a glass portion and the protectioncoating layer for protecting the glass portion, the arrayed opticalfiber ribbon being constituted by coating all the n (n is naturalnumber) optical fibers arranged in parallel by the collectively coatingresin layer; heating, melting, connecting and elongating the exposedglass portions of the optical fibers for every two to form elongatedportion; and fixing to a reinforcement member the glass portionssandwiched from the both sides of the elongated portion and theprotection coating layer outside of the exposed glass.

In the invention defined in claim 10, in a method according to claim 9,an adhesive having the viscosity of 50 to 200 P before the cure may beused for the fixing.

In the invention defined claim 11, in a method according to claim 9, anadhesive having thermosetting property and ultraviolet cure property maybe used for the fixing.

In the invention defined in claim 12, in a method of manufacturing anarrayed optical fiber coupler comprising the steps of removing coatingfrom 2n optical fibers (n is a natural number) to expose glass portions;arranging the optical fiber glass portions in parallel for every two;and after collectively melting and elongating the arranged opticalfibers, collectively fixing to a reinforcement member, the method ischaracterized in that said fixing comprises fixing with an adhesivehaving the viscosity of 50 to 200 P before the cure.

In the invention defined in claim 13, in a method according to claim 12,the adhesive may be replaced with an adhesive having thermosettingproperty and ultraviolet cure property.

In the invention defined in claim 14, in a method according to claim 12or 13, the 2n optical fibers may be of two tape type optical fiberribbons.

In the present invention, the influence to the melted, coupled andelongated portion can be prevented by not fixing the collectivelycoating resin layer to the reinforcement member or by fixing the resinlayer to the reinforcement member with a soft adhesive, even if thecollectively coating resin layer removes relatively to the glassportions.

In the present invention, by fixing the optical fibers with the resinhaving the viscosity of 50 to 200 P before the cure, any space in theresin surrounded by the optical fibers can be prevented from beinggenerated so that the coupler can be obtained with less characteristicchange for a heat cycle. Also, by using-both thermosetting type andultraviolet cure type resin as an adhesive, the resin hardness can beincreased even in the lower portion of the optical fibers, so that thecoupler can be obtained with the superior heat and humid resistancecharacteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C show an arrayed optical fiber coupler according tothe first embodiment of the present invention, FIG. 1A is a plan view,FIG. 1B is a cross sectional view taken along the II--II line, and FIG.1C is a cross sectional view taken along the III--III line;

FIG. 2 is a perspective view of a reinforcement case appliribbon to thefirst embodiment shown in FIGS. 1A, 1B and 1C;

FIGS. 3A, 3B and 3C show an arrayed optical fiber coupler according tothe second embodiment of the present invention, FIG. 3A is a plan view,FIG. 3B is a cross sectional view taken along the II--II line, and FIG.3C is a cross sectional view taken along the III--III line;

FIG. 4 is a perspective view of a reinforcement case appliribbon to thesecond embodiment shown in FIGS. 3A, 3B and 3C;

FIGS. 5A, 5B and 5C show an arrayed optical fiber coupler according tothe third embodiment of the present invention, FIG. 5A is a plan view,FIG. 5B is a cross sectional view taken along the II--II line, and FIG.5C is a cross sectional view taken along the III--III line;

FIG. 6 is a perspective view of a reinforcement case appliribbon to thethird embodiment shown in FIGS. 5A, 5B and 5C;

FIGS. 7A, 7B and 7C show an arrayed optical fiber coupler according tothe fourth embodiment of the present invention, FIG. 7A is a plan view,FIG. 7B is a cross sectional view taken along the II--II line, and FIG.7C is a cross sectional view taken along the III--III line;

FIGS. 8A and 8B are cross sectional views showing an example of a taperibbon appliribbon to a reinforcement structure in the arrayed opticalfiber coupler of the present invention, FIG. 8a shows a 2-arrayed taperibbon, and FIG. 8B shows a 8-core type of tape ribbon;

FIG. 9 is a diagram showing a group of units which are used to achievethe reinforcement structure in the arrayed optical fiber coupler of thepresent invention;

FIGS. 10A, 10B and 10C show the reinforcement structure in aconventional arrayed optical fiber coupler, FIG. 10A is a plan view,FIG. 10B is a perspective view of the reinforcement case used in thereinforcement structure shown in FIG. 10A, and FIG. 10C is a crosssectional view of a 4-core type tape ribbon;

FIG. 11 is a graph showing the change of coupling loss in a heat cycletest;

FIG. 12 is a graph showing the change of coupling loss under high humidand hot circumstance;

FIGS. 13A and 13B are cross sectional views showing an expanded crosssection structure of a fixed portion in the arrayed optical fibercoupler, FIG. 13A shows the structure in which the space surrounded bythe 4-core type optical fiber ribbon is filled with fixing resin, andFIG. 13B shows the structure in which the space is not filled with thefixing resin; and

FIG. 14 is a cross sectional view showing points P1 to P5 of the fixedportion shown in FIG. 13A where hardness is measured.

THE BEST MODE OF PREFERRED EMBODIMENTS

The embodiments of the present invention will be described below withreference to the accompanying drawings.

FIGS. 1A, 1B and 1C show an arrayed optical fiber coupler according tothe first embodiment of the present invention. More specifically, FIG.1A is the plan view of the coupler, FIG. 1B is the cross sectional viewof the coupler taken along the line II --II, and FIG. 1C is the crosssectional view of the coupler taken along the line III--III. FIG. 2 is aperspective view of a reinforcement case as a reinforcement member usedin the first embodiment.

The embodiment of the present invention will be described below withreference to the accompanying drawings.

Of constituent elements in the present embodiment shown in FIGS. 1A, 1B,1C, and 2, the same ones as those of the reinforcement structure in theconventional arrayed optical fiber coupler shown in FIGS. 10A, 10B and10C are assigned with the same reference numerals and the descriptionwill be omitted.

The present embodiment will be described with reference to a 4-core typeoptical fiber ribbon 1 shown in FIG. 10C. A collectively coating resinlayer 1a in the central portion of the 4-core type optical fiber ribbon1 is removed and optical fibers 2 are separated into for every twofibers. Next, a protection coating layer 2a of each of the opticalfibers 2 is removed such that a glass portion thereof is exposed.Preferably the protection coating layer 2a is not removed over theseparated optical fiber portion but removed in a minimum, inconsideration of strength stability. Another 4-core type optical fiberribbon 1 which is prepared in the same manner as described above toexpose the glass portions 2b is overlain on the above-mentionedribbon 1. The glass portions 2b of the corresponding optical fibers 2 ofthe optical fiber ribbons 1 are heated and melted and coupled to eachother. Then, the glass portions are elongated to form a melted, coupledand elongated section 2c having a small diameter as shown in FIG. 1A.Since the optical fibers 2 are separated for every two lines, a group isconstituted of 4 optical fibers 2 of the upper and lower ribbons 1 bythe melting, coupling and elongating process. Thus, the arrayed opticalfiber coupler composed of two groups of four optical fibers 2 can beobtained from the two overlain 4-core type optical fiber ribbons 1.

There is one of the features of the present invention in the structurein which such an arrayed optical fiber coupler is fixed to areinforcement case 3 shown in FIG. 2. That is, the reinforcement case 3shown in FIG. 2 has a partitioning wall 3c between the fixed walls 3b inthe central portion on the upper surface 3a of the reinforcement case 3shown in FIG. 10B so that a groove portion is divided into two groovesby the partitioning wall 3c. Each of the groups of four optical fibers 2is arranged such that the elongated portions 2c thereof are positionedin the central portion of one groove and the glass portions 2b and theprotection coating layers 2a of these optical fibers are fixed to thegroove via an adhesive layer 4. FIG. 1B shows the fixing structure ofthe four optical fibers 2 to the reinforcement case 3 and FIG. 1C showsa fixing structure of the glass portions extending from the above fixingstructure.

In the present embodiment, the collectively coating resin layer 1a ofthe optical fiber ribbon 1 is not fixed to the reinforcement case 3.Therefore, the influence due to distortion remained in the collectivecoating resin layer 1a from when the optical fiber ribbon 1 ismanufactured can be eliminated so that the degradation of transmissioncharacteristics can be avoided.

FIGS. 3A, 3B and 3C show the arrayed optical fiber coupler according tothe second embodiment of the present invention. FIG. 3A is a plan view,FIG. 3B is a cross sectional view of the coupler taken along the lineII--II, and FIG. 3C is a cross sectional view of the coupler taken alongthe line III--III. FIG. 4 is a perspective view of a reinforcement caseas a reinforcement member used in the present embodiment.

The difference of the second embodiment from the first embodiment ismainly in the groove structure of the reinforcement case 3. That is,three partitioning walls 3c are formed on the upper surface 3a of thereinforcement case 3 such that 4 grooves can be formed between the fixedwalls 3b with the same size. The elongated portion of a pair of opticalfibers 2 is arranged in each of the groove. The protection coatinglayers 2a and glass portions 2b of the optical fibers 2 are fixed by anadhesive layer 4 for every groove. The collectively coating resin layerof the arrayed optical fiber ribbon is also not fixed to thereinforcement case in the second embodiment, as in the first embodimentand hence the degradation of transmission characteristics can beavoided.

FIGS. 5A, 5B and 5C show the arrayed optical fiber coupler according tothe third embodiment of the present invention. FIG. 5A is a plan view,FIG. 5B is a cross sectional view of the coupler taken along the lineII--II, and FIG. 5C is a cross sectional view of the coupler taken alongthe line III--III. FIG. 6 is a perspective view of a reinforcement caseas a reinforcement member used in the present embodiment.

The difference of the third embodiment from the first embodiment ismainly in the structure of the reinforcement case 3 and in that twotypes of adhesive having different Young's moduli are used in the fixingof the coupler to the reinforcement case. The same 4-core type opticalfiber ribbon as in the first embodiment is used as the arrayed opticalfiber ribbon and the collectively coating resin layer of the ribbon 1 isalso fixed to the reinforcement case 3 by an adhesive layer 5 in thisembodiment. The adhesive layer 5 is softer than the adhesive layer 4 bywhich the protection coating layer 2a and glass portion 2b of theoptical fiber 2 are fixed to the reinforcement case 3. For this reason,even if the collectively coating resin layer 1a of the optical fiberribbon 1 is directly fixed to the reinforcement case 3, the transmissioncharacteristics are not degraded because the influence of distortionremained in the collectively coating resin layer 1a upon themanufacturing can be canceled or eliminated by the difference betweenthe adhesive layers 4 and 5 in the Young's modulus.

FIGS. 7A, 7B and 7C show the arrayed optical fiber coupler according tothe fourth embodiment of the present invention. FIG. 7A is a plan view,FIG. 7B is a cross sectional view of the coupler taken along the lineII--II, and FIG. 7C is a cross sectional view of the coupler taken alongthe line III--III.

The present embodiment indicates an example of the reinforcementstructure in the coupler in which the reinforcement case shown in FIG.10B is used. Also in the embodiment, the protection coating layer 2a andglass portion 2b of the optical fiber 2 of the 4-core type optical fiberribbon 1 are fixed to the reinforcement case 3 by the adhesive layer 4.This fixing does not concern with the fixing of the collectively coatingresin layer 1a of the optical fiber ribbon 1 to the reinforcement case3. Therefore, the coupler in the embodiment is not influenced by thedistortion remained in the collective coating resin layer 1a.

In the above embodiments, the 4-core type optical fiber ribbon is usedas the arrayed optical fiber ribbon. However, a 2-core type opticalfiber ribbon shown in FIG. 8A or a 8-core type optical fiber ribbonshown in FIG. 8B may be used. Although ultraviolet cure resin orthermosetting resin is used as a material for the collectively coatingresin layer used in the above embodiments, the material is not limitedto them. Further, the material of the reinforcement case needs to havethe line expansion coefficient as large as the quartz optical fiber andthe material such as quartz, liquid crystal plastics (LCP), fiberreinforced plastics (FRP), and invaliable alloys may be used. Theadhesive such as ultraviolet cure adhesive, thermosetting adhesive, andultraviolet ray and thermosetting adhesive may be used as the adhesivefor forming the adhesive layer.

FIG. 9 shows a group of units which are used to achieve the arrayedoptical fiber coupler according to the present invention. In the figure,a reference numeral 11 denotes an elongating stage, 12 an optical fiberclamper, 13 a microtourch, 14 a light source, 15 a power meter, and 16 areinforcement case supporting stage.

Next, the outline of processes in which the arrayed optical fibercoupler used in this invention is fixed to the reinforcement case usingthe units will be described below. For instance, the collectivelycoating resin layer 1a is removed from the central portion of thearrayed optical fiber ribbon 1 shown in FIG. 1A and the optical fibers 2are separated in plural. Then, the protection coating layer 2a of eachof the optical fibers 2 is removed to expose the glass portion 2b. Theexposed glass portions 2b are fixed by the optical fiber clamper 12 andheated by the microtourch 13 such that the glass portions 2b are meltedand coupled to each other. Thereafter, the coupled optical fibers 2 isreleased from the optical fiber clamper 12 and the coupled glassportions are heated and elongated while tension to them is maintained.At this time, the coupled glass portions are heated and elongated whilethe light branch state of the coupler is monitored using the lightsource 14 and the power meter 15 and when a predetermined light branchstate is achieved, the elongating operation is stopped. Next, thereinforcement case supporting stage 16 is moved to position thereinforcement case on the stage on a predetermined position and thecoupler is fixed to the reinforcement case by the adhesive. At thistime, it is important to fix the exposed glass portions on the bothsides of the elongated portion 2c as peripheral glass portions and theprotection coating layers outside of the peripheral glass portions tothe reinforcement case.

Next, the embodiments of the present invention will be described below,taking a particular example.

A 4-core type tape ribbon is prepared in which four optical fibers arecollectively coated, two layers protection coating being performed foreach of the 3 m band single mode optical fibers which has the differencebetween the core and the clad in refractive index of 0.3%, the corediameter of 8 μm, the clad diameter of 1.25μm. Using the 4-core typetape ribbon, a coupler is fabricated by the above group of units to havethe branch ratio of 50% in the light of wavelength of 1.3μm.

The reinforcement case made from crystalline glass (linear expansioncoefficient: 1.5×10⁻⁷ /° C.) is used.

Every two of the optical fibers are accommodated in one of the groovesof the reinforcement case having the structure shown in FIG. 2 and theglass portion of each optical fiber other than the elongated portion andthe protection coating layer are fixed to the reinforcement case toobtain the structure shown in FIG. 1A. Ultraviolet cure type adhesive isused in the fixing (embodiment 1).

Each of the optical fibers is accommodated in one of the grooves of thereinforcement case having the structure shown in FIG. 4 and the glassportion of each optical fiber other than the elongated portion and theprotection coating layer are fixed to the reinforcement case byultraviolet cure type adhesive to obtain the structure shown in FIG. 3A(embodiment 2).

Every two of the optical fibers are accommodated in one of the groovesof the reinforcement case having the structure shown in FIG. 6 and theglass portion of each optical fiber other than the elongated portion isfixed to the groove by ultraviolet cure type adhesive as well as thetape ribbon is fixed to the non-groove surface of the reinforcement caseby soft thermosetting type adhesive (Young's modulus: about 0.07 kg/mm²)to obtain the structure shown in FIG. 5A (embodiment 3).

Using the reinforcement case having the structure shown in FIG. 10B, theoptical fibers are fixed as in the first and second embodiments toobtain the structure shown in FIG. 7A (embodiment 4). That is, thecollectively coating resin layer of the tape ribbon is never fixed tothe reinforcement case but is outputted outside of the case.

On the other hand, the same arrayed optical fiber coupler as describedabove is fixed to the reinforcement case having the structure shown inFIG. 10B by ultraviolet cure type adhesive. In this case, thecollectively coating resin layer is also fixed to the same reinforcementcase by the same adhesive to obtain the structure shown in FIG. 10a (acomparison example).

A heat cycle test between -20 to 60° C. is performed for the couplers ofthe first to third embodiments and the comparison example under the samecondition. The transmission losses of the couplers are measured duringthe test using a laser emission diode (LED) having the wavelength of 1.3μm. The measuring result is shown in a table 1. In the table 1, "core1", core "2", "core 3", and "core 4" indicate the coupler numbers fromone end of the 4-core type tape ribbon. The value of greater change ofthe insertion losses at a straight port and a cross port is shown as thevalue of the loss change in the table 1.

                  TABLE 1                                                         ______________________________________                                                    embod-   embod-                                                                              embod- embod-                                                  iment    iment iment  iment                                       **          1        2     3      4     comparison                            ______________________________________                                        core 1  +0.11    +0.06   +0.04  +0.07 +0.18                                   core 2  +0.06    +0.13   +0.06  +0.12 +0.38                                   core 3  -0.03    +0.08   -0.05  +0.15 +1.09                                   core 4  +0.02    -0.02   +0.03  +0.06 +0.56                                   ______________________________________                                         **loss change (dB) during heat cycle                                     

As seen from the table 1, the comparison example has the remarkablecharacteristic change depending upon temperature and there is appearsthe influence of the distortion remained in the collectively coatingresin layer from when the tape ribbon is manufactured. On the otherhand, in the embodiments 1 to 3, because the influence of suchdistortion does not appear, the transmission characteristics of thecouplers are stable.

There is studied the characteristic change of the arrayed optical fibercouplers having the reinforcement structures by the adhesive asdescribed above under the particular circumstance tests (heat cycle testand high humid and hot test). That is, as a result of the study of thecharacteristic change in the above circumstance tests by the inventorsof the following facts are found. FIG. 13A shows a cross sectional viewof the fixed portion of the coupler which has the characteristic change(coupling loss change) of 0.06 dB in the heat cycle test shown in FIG.11 and is superior in the circumstance resistance characteristics andFIG. 13B shows a cross sectional view of the fixed portion of thecoupler which has the characteristic change of 0.5 dB in the same heatcycle test and is inferior in the circumstance resistancecharacteristics. As seen from FIG. 13A in the fixed portion of thesuperior coupler the space formed between 4 optical fibers 2b iscompletely filled with the adhesive layer 4 and on the contrary as seenform FIG. 13B in the fixed portion of the inferior coupler the spaceformed between 4 optical fibers 2b is not completely filled with theadhesive layer to form a cavity 6. In the heat cycle test when thecoupler is located in low temperature a small bending stress would acton each optical fiber (125 μmφ) 2b because of ununiform expansion orcontraction of the resin so that the transmission characteristics arechanged. The inventors fabricate samples in various viscosities of resin(adhesive) of the fixed portion in order to eliminate the generation ofthe cavity 6 and thereby the characteristic change in the heat cycletest. The following table 2 indicates the result.

It seen from the above table 2 that the resin (adhesive) viscosity forfixing the optical fiber is preferably in a range of 50 P to 200 P. Thatis, the types of resin c to e are suitable for the resin (adhesive) forfixing the optical fibers of the arrayed optical fiber coupler accordingto the present invention.

                  TABLE 2                                                         ______________________________________                                        Relation of the generation rate of cavity and fault                           by heat cycle test to resin (adhesive) viscosity                                                               (ratio of of                                                                  characteristic                               (type                (generation rate                                                                          change (0.2 dB                               of resin)                                                                             (viscosity)  of cavity)  or more)                                     ______________________________________                                        a       800 P        60%         50%                                          b       400          20          10                                           c       200           5           0                                           d       100           0           0                                           e        50           0           0                                                   (not easy to coat)                                                    f        30                                                                           (cannot coat)                                                         ______________________________________                                    

Next, The optical fiber fixed portion was cut as in the above and theresin hardnesses in the cross section were measured by a micro FTIR(Fourier transformation type infrared spectrometer). In FIG. 14 thehardness in the measuring point P1 was 95%, P2 96%, P3 93%, P4 88%, andP5 70%. As seen from FIG. 14, it was found that the hardness was lack inthe lower portion of the optical fiber (P4 or P5). Because the opticalfibers are collectively fixed, the light intensity would be weak in thelower portion of the optical fibers so that the cure of the resin isinsufficient. If the cure of the resin is insufficient, it is expectedthat a portion where polymerization is not caused reacts with water sothat the deterioration of the resin is caused under a high humid and hotcircumstance.

The inventors fabricated samples using ultraviolet cure andthermosetting resin such that the hardness of the resin in the lowerportion of the optical fibers was the same as that of other portions.The following table 3 indicates the result. The symbol "*" in the table3 indicates the high humid and hot test in the ambient of humidity of90% at 60° C. for 100 hours.

                  TABLE 3                                                         ______________________________________                                        Relation of change in high humid and hot test                                 to type of resin and hardening condition                                                             (characteristic                                        (type of     (hardening                                                                              change upon high humid                                 resin)       condition)                                                                              and hot test)                                          ______________________________________                                        UV           short     0.13 dB                                                UV           long       0.1 dB                                                UV + thermo  short     0.05 dB                                                ______________________________________                                    

It is found from the table 3 that ultraviolet ray and thermosetting typeresin is good in characteristic and preferable in productivity.

Next, the high humid and hot test in the ambient of humidity of 90% at60° C. for 100 hours was performed for the couplers of the embodiments 1and 3 in which the ultraviolet cure adhesive was not used. A monitorwavelength was 1.31 μm and the change of transmission loss was measuredfor each "optical fiber" of each coupler. The measuring result is shownin a table 4. In the table 4, "fiber 1", "fiber 2", "fiber 3" and "fiber4" are the same as in the table 1.

                  TABLE 4                                                         ______________________________________                                        Result of high humid and hot test                                                        embodiment 1                                                                              embodiment 2                                           ______________________________________                                        fiber 1      0.05 dB       0.03 dB                                            fiber 2      0.04          0.05                                               fiber 3      0.06          0.03                                               fiber 4      0.08          0.02                                               ______________________________________                                    

As seen from the table 4, it is found that the couplers of theembodiments 1 and 3 have extremely small characteristic change.

Possibility of Industrial Application

As described above, according to the present invention, the protectionof the coupler structure can be reinforced and the stabilization oftransmission characteristics can be achieved because the influence ofdistortion remained in the collectively coating resin layer of thearrayed optical fiber ribbon can be eliminated. The optical fibercoupler added with such a reinforced structure can sufficiently copewith the recent high density optical communication line by the stabilityof the transmission characteristics.

In addition, according to the present invention, by fixing the opticalfibers with resin having a viscosity of 50 P to 200 P before cure, thearrayed optical fiber coupler can be obtained in which a cavity can beprevented from being generated in a portion surrounded by the opticalfibers with less characteristic change in heat cycle test and withsufficient circumstance resistance characteristics.

Further, according to the present invention, by using ultraviolet rayand thermosetting type resin as an adhesive for fixing the opticalfibers, the arrayed optical fiber coupler can be obtained with superiorhigh humid and hot characteristic and with sufficient circumstanceresistance characteristics because the hardness of the resin can beincreased even in the lower portion of the optical fibers.

What is claimed is:
 1. An arrayed optical fiber coupler comprising:twoarrayed optical fiber ribbons that have been connected by melting,bonding, and elongating glass portions of each arrayed optical fiberribbon, each arrayed optical fiber ribbon including:a plurality ofoptical fibers being arranged in parallel to each other, each opticalfiber including one of the glass portions and a corresponding protectioncoating layer, and a resin coating layer that coats each of theplurality of optical fibers; and a reinforcement structure including afirst reinforcement member to which both a portion of the glass portionsand the corresponding protection coating layers are affixed by an firstadhesive layer, wherein the resin coating layer and the firstreinforcement member are not fixed to each other.
 2. An arrayed opticalfiber coupler as claimed in claim 1, wherein the arrayed optical fibercoupler further comprises a second reinforcement member to which theresin coating layer is affixed by a second adhesive layer, wherein thesecond adhesive layer is different from the first adhesive layer.
 3. Anarrayed optical fiber coupler as claimed in claim 2, wherein adhesivematerial in the second adhesive layer has a Young's modulus of 1 kg/mm²or less.
 4. An arrayed optical fiber coupler as claimed in claim 1,wherein the two arrayed optical fiber ribbons are affixed to the firstreinforcement member only by affixing the portion of the glass portionsand the corresponding protection coating layer to the firstreinforcement member.
 5. An arrayed optical fiber coupler as claimed inany one of claims 1 to 4, wherein the reinforcement member has a groovefor arranging two of the plurality of optical fibers in parallel.
 6. Anarrayed optical fiber coupler as claimed in claim 1, wherein the firstadhesive layer comprises an adhesive having a viscosity of 50 to 200 Pbefore being cured.
 7. An arrayed optical fiber coupler as claimed inclaim 1, wherein the adhesive layer comprises an adhesive having athermosetting property and a ultraviolet cure property.
 8. A method ofmanufacturing an arrayed optical fiber coupler comprising the stepsof:removing a resin coating layer and a plurality of protection coatinglayers from two arrayed optical fiber ribbons so as to expose glassportions, wherein:each arrayed optical fiber ribbon includes a pluralityof optical fiber, which are arranged in a parallel manner, and the resincoating layer, which coats each of the optical fibers, and each opticalfiber includes one of the glass portions and one of the protectioncoating layers; heating, melting, connecting and elongating two of theexposed glass portions so as to form an elongated portion; and fixingportions of the glass portions that are located on both sides of theelongated portion and the protection coating layer to a reinforcementmember.
 9. A method as claimed in claim 8, wherein the fixing stepincludes the use of an adhesive having a viscosity of 50 to 200 P beforebeing cured.
 10. A method as claimed in claim 8, wherein the fixing stepincludes the use of an adhesive having a thermosetting property and anultraviolet cure property.
 11. A method of manufacturing an arrayedoptical fiber coupler, comprising the steps of:removing, from 2n opticalfibers, protection coating layers so as to expose glass portions of theoptical fibers, wherein n is a natural number; arranging the exposedglass portions in a parallel manner; and after melting and elongatingthe arranged exposed glass portions, collectively fixing the glassportions and the protection coating layers to a reinforcement member,wherein said fixing step includes the use of an adhesive having aviscosity of 50 to 200 P before being cured.
 12. A method as claimed inclaim 11, wherein the adhesive is replaced with an adhesive that has athermosetting property and an ultraviolet cure property.
 13. A method asclaimed in claim 11 or 12, wherein the 2n optical fibers are part of twooptical fiber tape ribbons.